Water Well Journal

March 2015

Water Well Journal

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In some instances, both methods are used to seal the same pond. These ponds are typically privately owned for cosmetic land improvement, livestock, or stock ponds used for fishing. The use of bentonite in geosynthetic liners requires gluing or needle felting the bentonite between two sheets of special fabric or gluing the bentonite directly to a plastic sheet. By in- corporating the bentonite into a fabric sheet, it is distributed evenly, held in place, and protected. These characteristics also enable the barrier to be applied to an area by rolling out the liner over the ground to be pro- tected. This method results in a highly uniform, engineered construction material that can deliver consistent and reliable performance across a variety of projects and applications. The bentonite liner should also be properly prepared. In many instances, after the mat has been placed and before the retention water is collected, it is recommended the bentonite be hydrated with local freshwater. In this way, the clay struc- ture can fully expand while in its native, sodium bentonite form. After the liner is in contact with various aqueous contami- nants (such as trace hydrocarbons and aromatics, high total dissolved solids, high water hardness, and trace heavy met- als), the established filter cake will limit the migration of the contaminants to the topmost region of the clay layer and may greatly prolong the lifespan of the liner. For highly contaminated waters, the addition of certain polymers to the bentonite can aid in the integrity of the hy- drated filter cake and increase the resistance of the liner to the extreme conditions. When high concentrations of hydrocar- bons, aromatic compounds, and other organics are expected, organically treated clay (organoclay) can be placed in a liner in the same way that conventional bentonites are applied. When both aqueous and organic contaminants are expected, a combination of geosynthetic clay liner types with various clay packages can be used to sequentially address all water issues. Benefits of Wyoming Sodium Bentonite over Other Clay Types The sodium-rich bentonites of the northern region of Wyoming have long been valued for their high native purity and superior swelling capacity (Figure 1). Consequently, these clays are used throughout the world in many industries includ- ing oilfield and industrial drilling, iron ore pelletizing, wine clarification, animal litter, construction slurry walls, foundry clays, and cosmetics. The critical feature of these clays is the occurrence of montmorillonite in Wyoming bentonite, with 75% of its cation exchange capacity naturally occupied by sodium cations. 26 March 2015 WWJ waterwelljournal.com BENTONITE from page 25 Figure 1. An exposed formation of Wyoming bentonite during pit operations. Figures 2 and 3. A typical geosynthetic clay liner mat before and after hydration. The before image is shown in the top photo. The bentonite layer expands to as much as three times its original height and absorbs more than twice its weight in water. (bottom photo)

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